Apparatus and method for navigating vehicle to destination using display unit

Abstract: A bird's eye view commonly used in a flight simulation is applicable to an apparatus and method for navigating a vehicle running on a set route of travel to a set destination using a (color) display unit according to the present invention. The bird's eye view of a road map surrounding a present position of the vehicle has a viewing point placed at a predetermined position on an upper sky in a direction opposite to the set destination with the present position of the vehicle as a reference and has a line of sight looking down over the road map so that a part of the road map surrounding the present position of the vehicle can be viewed in an extended scale form and the remaining part of the road map remote from the present position and nearer to the set destination can be viewed in a gradually reduction scale form.

Description: The invention relates to an apparatus for navigating a vehicle using a display unit according to the preamble of claim 1. Various types of vehicular navigating systems (also called, vehicular route guidance apparatuses) in which an optimum route of travel from a start point of the vehicle to a destination is searched and derived and both of the optimum route and a present position of the vehicle are displayed on a display screen of a display unit have been proposed. Fig. 1A exemplifies a displayed image in a case of one of the previously proposed vehicular navigating systems. As shown in Fig. 1A, the present position of the vehicle is superimposed and displayed on the display image screen with an arrow mark and with its surrounding portion of the arrow marked present position encircled by a dotted line. Then, when an operator operates a predetermined switch, a range encircled with the dotted line is displayed in an extended form as shown in Fig. 1B. This permits the operator to recognize a road (traffic) situation surrounding the present position in details. In this way, when the displayed images are exchanged from Fig. 1A to Fig. 1B and vice versa, it is always necessary to operate the predetermined switch. This makes the operation troublesome. On the other hand, another previously proposed navigating system in which road maps having different reduction of scales are simultaneously displayed on the display image screen, this display form being, so-called, superimpose displayed patterns, as shown in Fig. 2. Fig. 2 exemplifies the displayed image screen of the other previously proposed vehicular navigating system, with intersection situations surrounding the present position of the vehicle being displayed in the extended scale form on a right upper corner of the displayed image screen. This other previously proposed navigating system permits the vehicular occupant to recognize the road map having a wide range of view with the present position of the vehicle as a center and to recognize the road (traffic) situation surrounding the present position of the vehicle in details. However, since, in the displayed image screen shown in Fig. 2, the part of the road map has been displayed on the right upper corner of the displayed image screen in the extended scale form, the actual road map to be displayed on the right upper corner of the displayed image screen cannot be viewed from the displayed image screen (is hidden by the extended part of the road map). Hence, in a case where, for example, the vehicle driver tries to turn a right corner corresponding to the displayed portion of the hidden part (not displayed), the vehicle driver cannot recognize a road (traffic) situation in the forward direction. This makes the vehicle driver inconvenient. EP-A-378 271 discloses a method for displaying a part of a topographic map in a perspective manner and a device suitable for performing such a method. Upon determining a current position of a driving vehicle, a relevant part of the map is selected with respect to the direction of travel of the vehicle. The selected part of the map is displayed, under the influence of a coordinate transformation, in a central projection from an apparent point of view which is situated outside the vehicle and above the relevant part of the surface of the earth (bird's eye view). It is the object of the present invention to provide an apparatus for navigating a vehicle using a display providing a larger variety of selectable bird's eye views. This object is solved by the subject matter of claim 1. A further advantageous embodiment of the invention is subject matter of the subclaim. In the following, preferred embodiments of the invention will be described in more detail by referring to the accompanying drawings, wherein Figs. 1A and 1B are explanatory views of examples of road map on a display image screen of a display unit in a former previously proposed navigation system described in the BACKGROUND OF THE INVENTION. Fig. 2 is an explanatory view of another example of road maps simultaneously displayed on the display image screen of the display unit in a latter previously proposed navigation system described in the BACKGROUND OF THE INVENTION. Fig. 3A is a schematic explanatory view of a bird's eye view prepared from a viewing point for explaining the bird's eye view applicable to an apparatus and method for navigating a vehicle using a display unit according to the present invention. Fig. 3B is a schematic explanatory view of a bird's eye view in a three-dimensional coordinate system with a viewing point on a Z axis. Fig. 4 is an explanatory view of an example of a displayed image screen in which the present position of the vehicle, a set optimum route of travel to a destination are displayed with the bird's eye view shown in Fig. 3. Fig. 5 is a schematic circuit block diagram of the apparatus for navigating the vehicle using the display unit in a preferred embodiment according to the present invention. Fig. 6 is an operational flowchart for explaining an operation of the navigating apparatus shown in Fig. 5. Fig. 7 is an operational flowchart for explaining a subroutine of a step S5 in Fig. 6. Fig. 8 is an explanatory view for explaining a displayed image on a display image screen in the case of the first embodiment. Fig. 9 is an explanatory view for explaining the displaying method executed in the subroutine of the step S5 in Fig. 7. Fig. 10 is an operational flowchart of a subroutine of a step S5 in Fig. 6 in a case of the preferred embodiment of the vehicular navigating apparatus according to the present invention. Fig. 11 is an explanatory view for explaining a positional relationship between a viewing point and the present position of the vehicle in the case of the preferred embodiment shown in Fig. 12. Fig. 12 is an explanatory view for explaining a relationship between a direction of a line of sight and a range of the road map displayed on the display unit in the case of the embodiment. Reference will hereinafter be made to the drawings in order to facilitate a better understanding of the present invention. Before explaining the preferred embodiment of an apparatus and method for navigating a vehicle with a display unit according to the present invention, a basic concept of the invention will be described with reference to Figs. 3A, 3B and 4. Fig. 3A and 3B show explanatory views for explaining a bird's eye view (E) from a predetermined position on an upper sky looking down to a road map as a viewing point to which the present invention is applicable. The bird's eye view display is carried out as if the road map were viewed from an upper sky looking down thereof and is widely used in, for example, a flight simulation. In Fig. 3A, a plane M denotes a road map and a rectangular shape a, b, c, and d denotes a displayed range through a display unit 5. Suppose that, in Figs. 3A and 3B, a viewing point (E) is set on a position as shown in Figs. 3A and 3B. the range of road map which can be viewed through the rectangular shape a, b, c, and d corresponds to a trapezoid region A, B, C, and D shown in Figs. 3A and 3B. That is to say, from the position of the viewing point, a map data whose range is considerably wider than that of the rectangular shape a, b, c, and d can be viewed. In this way, the bird' eye view is displayed on the display image screen of the display unit 5 as if the shown trapezoid region A, B, C, and D were seen on its image from the position of the viewing point E of Figs. 3A and 3B. Fig. 4 shows an example of the display of the bird's eye view on the road map surrounding an optimally set route of travel from the present position of the vehicle to the destination (a position of the road map to which the vehicle is finally to reach). As shown in Fig. 4, the viewing point (E) is placed at the predetermined position of the upper sky in a direction opposite to the set destination and from the viewing point (E) thus placed, a destination direction is looked down through its line of sight. When the viewing point is placed at such a position as described above, an image such that a reduction scale percentage of the road map is continuously increased as the eye is approached nearly from the destination to the present position of the vehicle can be displayed as shown in Fig. 4. That is to say, the optimally set route of travel can be displayed up to the place nearer to the destination together with the surrounding position of the present position displayed in the extended scale form. (First Embodiment) Fig. 5 shows a schematic circuit block diagram of an apparatus for navigating a vehicle using a display unit 5 in a first embodiment according to the present invention. In Fig. 5, a direction sensor 1 is connected to an interface circuit 10 and is arranged for, for example, detecting a geomagnetism at a position at which the vehicle is present on the basis of the North direction so as to determine a forward direction of the vehicle. The direction sensor 1 is exemplified by a United States Patent No. 4, 442, 609 issued on April 17, 1984 (, the disclosure of which is herein incorporated by reference). A vehicle speed sensor 2 is connected to the interface circuit 10. The vehicle speed sensor 2 is disposed on a power transmission output shaft and outputs a pulse train signal whose predetermined pulse number is varied depending on a vehicle speed. A map storing memory 3 serves to store a road map data including an intersection network data, the road map data further including positional information indicating nodes representing the intersections, curved road points, and so forth, route path lengths of roads connecting between the roads, and character data including name of places. A CPU (Central Processing Unit) 4 is connected to the interface circuit 10 for preparing the bird's eye view display data on the road map according to a series of processing shown in Figs. 6 and 7 which will be described later. A ROM (Read Oly Memory) 6 is connected to the interface circuit 10 and used for storing control program, for example, shown in Figs. 6 and 7, to be executed by the CPU 4. A RAM (Random Access Memory) 7 is connected to the interface circuit 10 and used for storing a series of calculation results executed by the CPU 4. A V-RAM (Video RAM) 9 is connected to the interface circuit 10 and used for storing the bird's eye view display data prepared by the CPU 4, the viewing point of and line of sight of the bird's eye view to be displayed on the display unit 5 being changed according to the content of the V-RAM 9. An operator keyboard 8 is connected to the interface circuit 10. The interface circuit 10 is connected to every computer peripheral circuit element described above. It is noted that as soon as an operator (vehicle driver or occupant) operates an ignition key inserted into an ignition key switch of the vehicle to turn on either of ACC, IGN, or START portion of the ignition key switch of the vehicle, the CPU 4 starts the control routine shown in Fig. 6. An operation of the first embodiment will hereinafter be described with reference to Figs. 6 and 7. At a step S1 of Fig. 6, the CPU 4 reads the destination at which the vehicle is finally to reach and which is input through the keyboard 8. At a step S2 of Fig. 6, the CPU 4 measures the number of pulses per time output from the vehicle speed sensor 2 or a pulse period of the pulse train of the vehicle speed sensor 2 so as to determine the running speed of the vehicle and measures the number of pulses so as to determine the running distance for which the vehicle has run. Next, the CPU S2 calculates a running trajectory on the basis of the forward direction of the vehicle detected by means of the direction sensor 1 and of the vehicle running distance and specifies the present position of the vehicle by means of a map matching technique between the running trajectory and road map data stored in the road map memory 3. At a step S3, the CPU 4 calculates an optimum route of travel of the vehicle from a start point of the vehicle which is specified at the step S2 to the destination by means of a well known Dikustra technique by searching for the route of paths from the start point to the destination. This Dikustra technique is exemplified by a Japanese Patent First Publication (Unexamined) No. Showa 62-86499 published on April 20, 1987 (or by a United States Patent Application Serial No. 08/302, 028 filed on September 9, 1994.) At a step S4, the road map data surrounding the searched optimally set route of travel is read from the road map data memory 3 on the basis of the calculated optimum route of travel by the CPU 4 and is stored in the RAM 7. At a step S5, the CPU 4 determines a position of the viewing point to display the bird's eye view by means of the series of processing shown in Fig. 7. When the step S5 is processed, the road map range to be displayed on the display unit 5 is determined. At a step S6, the CPU 4 transforms the road map data into the bird's eye view data. That is to say, as shown in Fig. 3A, the CPU 4 transforms the road map data within the trapezoid region A, B, C, and D into the bird's eye view data to be displayed on the display unit 5 according to the positional relationship between the position of the viewing point E, the position of the rectangular shape of a, b, c, and d, and road map position. The coordinate system transformation is such that the part of the road map corresponding to a side BC is displayed on a lower side of the display unit 5, a part of the road map corresponding to a side AD is displayed on an upper side of the display unit 5, and, in addition, the reduction scale percentage is increased as the part of the image corresponding to the side AD becomes nearer to that corresponding to the side BC. It is noted that, the horizontal distance of the position of the viewing point E with respect to the place M and its height in the Z axis direction are defined so that, the sides BC and AB give 300 m and 10 Km in their actual dimensions, respectively, and a distance from the side CD to the side AD gives 10 Km in its actual dimension. At a step S7, the CPU 4 stores the bird's eye view display data prepared at the step S6 into the V-RAM 9. Consequently, the road map within the trapezoid region ABCD of Fig. 3A can be displayed on the display unit (display) 5 as shown in Fig. 8. At a step S8, the CPU 4 reads character data on, for example, names of places and name of intersections included in the road map data within the trapezoid region ABCD of Figs. 3A and 3B and temporarily stores the V-RAM 9, thus character information such as names of places being superimposed on the road map displayed on an image screen of the display unit 5. At a step S9, the CPU 4 calculates the present position of the vehicle from a running distance and a forward direction from the position detected at the step S2 using the direction sensor 1 and vehicle speed sensor 2. At a step S10, the coordinate system of the present position of the vehicle calculated at the step S9 is transformed in the same way as the step S6 so that the present position of the vehicle denoted by the vehicle mark data is stored into the V-RAM 9. Consequently, as shown in Fig. 11 or Fig. 4, the arrow-marked present position of the vehicle is displayed. At a step S11, a movement vector quantity of the vehicle upon the display of the road map at the step S7, that is to say, a movement direction and a movement distance are detected and if the movement vector quantity has exceeded a predetermined quantity, the routine goes to the step S4 so that an updating of the bird's eye view on the display image screen of the display unit 5 is carried out. Consequently, the surrounding place around the present position of the vehicle is always extensively displayed on a lower end area of the display image screen of the display unit 5 in the scale extended form and the rewriting of the bird's eye view to be displayed on the image screen of the display unit 5 is carried out along with the running of the vehicle on the set route of travel. Fig. 7 shows a detailed processing flowchart of the step S5 in Fig. 6. Fig. 9 shows an example of the road map data read out from the road map memory 3 at the above-described step S4 in which a hairpin curve, i.e., U-shaped turning road forwarding in the direction opposite to that of the set destination is present on the set (optimum) route of travel to the set destination denoted by a bold line. The explanation of Fig. 7 will be described below with reference to Fig. 9. At a step S21 of Fig. 7, the CPU 4 determines a direction of a line segment OD connecting the present position of the vehicle O detected at the step S2 and set destination D read at the step S1, as appreciated from Fig. 9. At a step S22 of Fig. 7, the CPU 4 determines a direction of a straight line (V) (as shown in Fig. 9) which is perpendicular to the line segment OD and is passing through the present position of the vehicle denoted by O in Fig. 9. At a step S23, the CPU 4 detects a position of a crossing point Dc between the straight line (V) and optimum route of travel L. At a step S24 of Fig. 7, the CPU 4 derives each of an area Sm of a triangular region ODcD with each node Dm (wherein, 1≦m≦n, n denotes a total number of the nodes) present on the part of the set (optimum) route of travel between the present position O of the vehicle and the crossing point Dc as a vertex of the triangular region and with the line segment ODc as a bottom side. At a step S25, the CPU 4 determines a maximum value of the derived Sm (wherein, 1 ≦m ≦ n) at the step S24 and derives a height of its corresponding triangular region from which the maximum value described above is determined, the height hmax being defined as a vertical distance from the line segment ODc to the node Dm). At a step S26, the CPU 4 determines a position of a point Dh hmax away from the present position of the vehicle O and whose angle of direction is 180 degrees different from the set destination D. At a step S27, the CPU 4 determines whether any point at which the line segment ODh is intersected with the set route of travel L is present. In the case of Fig. 9, since the line segment ODh is intersected with the set route of travel L at the point K, the positive acknowledgment is determined at the step S27 and is transferred to a step S28. At the step S28, the CPU 4 derives each area S1m of a triangular region ODhDm with each node Dm placed at a left side of the line segment ODh (wherein, 1≦m≦p, p denotes a total number of nodes present at the left side of the line segment ODh) as its vertex and derives each area of another triangular region ODhDm with the line segment ODh as its bottom side and each node. Dm (wherein, 1≦ m ≦ q, q denotes a total number of nodes present at the right side of the line segment ODh) as its vertex. At a step S29 of Fig. 7, the CPU 4 determines the maximum values of the areas from each area S1m (wherein, 1≦ m ≦ p) and each area Srm (wherein, 1≦m≦ q). The CPU 4, then, heights of w1 and wr of the triangular regions determined therein and derives a sum W of the heights w1 and wr. Then, the subroutine goes to a step S30. At a step S30 of Fig. 7, the viewing point (E) of the bird's eye view is set at a position of an upper sky from which the road map including the range of the triangular region X in which the derived W at either the step S29 or S32 are longitudinal length and lateral length can be looked down over. For example, when the height w2 is larger than the height w1, as shown in Fig. 9, the upper sky above the point (E) shown in Fig. 9 and placed at the right side of the line segment ODh is set as the viewing point (E) of the bird's eye so as to enable the whole rectangular region X to be looked down over. As described above, in the first embodiment, the line of sight from the viewing point (E) of the bird's eye view is varied according to a length and direction of the hairpin curve on the set route of travel and the bird's eye view is displayed on the display image screen of the display unit 5. Thus, all of the hairpin curves can be displayed thereon. Although, in the first embodiment, the viewing point (E) is set at the position so as to enable the whole rectangular region enclosing the hairpin curve to be viewed, the height of the viewing point and line of sight direction may alternatively be varied according to the length and direction of the hairpin curve. For example, in the case where the hairpin curve is relatively long, the displayed region on which the set destination direction can be displayed becomes narrower if all of hairpin curves on the set route of travel are displayed. In this case, only a part of the hairpin curve displayable region may be displayed, for example, as shown in Fig. 4. Alternatively, a special switch used to determine whether the operator desires for the display unit 5 to display the hairpin curve region may alternatively installed so as to be connected to the interface circuit 10. In addition, in place of the operation keyboard 8, a touch panel switch integrated with the display unit 5 may be used. Furthermore, the keyboard 8 may serve to directly input the set destination into the interface circuit 10. Although, in the embodiment, the present position of the vehicle is specified using the direction sensor 1 and vehicle speed sensor 2, the present position of the vehicle may be determined according to the input information through the keyboard 8. Or alternatively, a GPS (Global Positioning System) using electromagnetic waves from a plurality of satellites may be used to specify the present position of the vehicle. Although, in the embodiment, the optimally (set) route of travel is derived from the calculation of the CPU 4 (step S3 of Fig. 6), the vehicle may be guided in accordance with an input route of travel prepared by the keyboard 8 and the bird's eye view can accordingly be displayed. Fig. 12 shows an explanatory view how the range of the road map displayed on the display image screen is varied when a line of sight direction of the bird's eye is varied for each of 30° . Each of trapezoid regions EFGH, IJKL, and MNOP denotes a road map range to be displayed on the display image screen in each of the lines of sights of the bird's eye views. Although a length of the distance of the set route of travel LL shown in Fig. 12 and displayed on the image screen which provides the maximum corresponds to the trapezoid region ABCD shown in Fig. 11 (or Figs. 3A or 3B), the length of the set route of travel displayed within each trapezoid region is accordingly varied if the general direction of the whole set route of travel is different. That is to say, if the bird's eye view is displayed without consideration of the general direction of the set route of travel, the set route of travel cannot be displayed with a sufficient length thereof. Fig. 10 shows a subroutine of the step S5 shown in Fig. 6 in a case of the preferred embodiment according to the present invention. The main routine is the same as that shown in Fig. 6 of the embodiment and the hardware structure of the vehicular navigation apparatus in Fig. 6 is the same as shown in Fig. 5. It is noted that at the step S6 of Fig. 6, the CPU 4 carries out the coordinate system transformation of the road map data within the range of the trapezoid region ABCD according to the position of the viewing point E and positional relationship between the position of the rectangular abcd and road map position into the data to be displayed on the display image screen of the display unit 5. Specifically, the part of the road map at a side BC is displayed on a lowest side of the display image screen of the display unit 5 and the part of the road map at a side AD is displayed on an upper side of the display image screen. In addition, the reduction scale percentage becomes large as the position approached from the side AD to the side BC. It is noted that the viewing point position and height of the viewing point are defined such that, for example, the sides of BC and AB are 300m and 10 Km in their actual dimensions and the distance from the side CD to the side AB is 10 Km in the actual dimension. It is also noted that when the series of processing of Fig. 10 are executed, the viewing point S is set on an upper sky in a direction of (180° + °) with the North direction of the road map as  = 0° and on an upper sky above a point T which is remote a predetermined distance from the present position of the vehicle G, as shown in Fig. 11. Then, the rectangular region abcd indicating the display range is set at a predetermined position between the viewing point S and present position of the vehicle G. At a step S21A of Fig. 10, the CPU 4 initializes such that  = 0° and total values L (wherein, = 0°, 30°, ---, 300°) of the path lengths of route links are all zeroed. The term route links denote roads (links) connecting between the adjacent nodes on the set route of travel. In the embodiment, the route links of m-th numbers on the set route of travel are denoted by l 1 through l m in the order from the present position to the destination. At a step S22A, a variable n is set to zero. The variable n denotes a variable to specify one of the route links on the set route of travel. That is to say, l n denotes the n-th number route link from the present position of the vehicle. At a step S23A, the CPU 4 reads the road map data in a range of the road map which can be viewed through the rectangular abcd, with the line of sight directed toward the direction  from the viewing point position. That is to say, the CPU 4 reads the road map data in the range of the trapezoid region ABCD shown in Fig. 11. At a step S24A, the CPU 4 determines whether the data related to the route link l n in the road map data read at the step S23A, that is to say, determines whether the route link l n can be displayed on the display image screen of the display unit 5 when the bird's eye view is displayed with the line of sight direction set as . If the determination is acknowledged at the step S24A, the subroutine goes to a step S25A in which the path length of l n is added to the total value of the route path length L . Then, the subroutine goes to a step S26A. On the other hand, if the determination is not positive acknowledgment at the step S24A, the subroutine goes to the step S26A in which the variable n is added to one. At a step S27A, the CPU 4 determines whether the variable n is larger than m indicating the total number of the route links. If No at the step S27A, the subroutine goes to the step S24A and if Yes at the step S27A, the subroutine goes to a step S28A. At the step S28A, the line of sight direction  is added to 30°. At a step S29A, the CPU determines whether  = 360°. If No at the step S29A, the subroutine returns to the step S22A. If Yes at the step S29A, the subroutine goes to a step S30A. At the step S30A, the CPU 4 selects one of the total values which is largest from the respective route lengths of L0, L30, L60, ----, L330. The corresponding angle of  is stored in the RAM 7. Then, this subroutine is ended. In the embodiment shown in Fig. 10, the direction of line of sight is varied for each 30 degrees, the total values of the route path lengths of the route links displayed on the display image screen of the display unit 5 are derived for the respective directions of the line of sight, and one of the directions of line of sight is automatically selected which provides the displayed longest set route of travel. Although, in the embodiment shown in Fig. 10, the comparison of the total values of the route lengths on the set route of travel L with the directions of the line of sights varied for each 30°, the value of the angle may not be fixed as 30°.

Claims: An apparatus for navigating a vehicle using a display unit (5), comprising: a) road map storing means (3) for storing a road map data related to a road map; b) vehicle position detecting means (1, 2) for detecting a present position of the vehicle; c) vehicle destination setting means (8) through which a destination to which the vehicle is desired to reach is set on the road map; d) start point setting means (1, 2) for setting a starting point location on the road map at which the vehicle is to start based on the detected present position of the vehicle; e) route of travel setting means for setting a route of travel on the road map from the start point to the set destination; and f) display control means (4, 9) for controlling an image of the road map surrounding the route of travel set which is displayed on the display unit in a form of a bird's eye view such that the bird's eye as a viewing point (E) is referenced at a predetermined position on a raised plane from said road map and offset in a direction opposite to the set destination with respect to the present position of the vehicle, and the road map surrounding the set route of travel is being displayed to appear to a user as looking down over the road map from the bird's eye, g) bird's eye view generating means for generating a plurality of the bird's eye views each achieved when the bird's eye as a viewing point is placed on an upper sky looking down from the viewing point and each bird's eye view having a different height to the earth; and h) bird's eye view selecting means characterized in that the bird's eye view generating means further generates bird's eye views respectively having different lines of sight towards the set destination, even if the height to the earth is kept constant; and that the bird's eye view selecting means selects that bird's eye view which has the longest distance of the set route of travel to be displayed on the display unit by said display control means. The apparatus for navigating a vehicle using a display unit as claimed in claim 1, characterized in that said bird's eye view generating means generates a plurality of bird's eye views having a respectively different line of sight, said bird's eye view selecting means drives a total value (L), equal to the sum of the length of each route link between nodes on the set route of travel displayed on the respective bird's eye view, for each different line of sight and said bird's eye view selecting means selects one of the respective bird's eye views as being one of the lines of sight in the direction through which the total value (L) is a maximum.

Inventors: IWASAKI MASAYASU, KISHI NORIMASA, KOSAKA AKIO, NAKAYAMA OKIHIKO, TSUDA HIROSHI, WATANABE MASAKI, YAMADA KIYOMICHI, YATSUGI YOSHITAKA, IWASAKI, MASAYASU, KISHI, NORIMASA, KOSAKA, AKIO, NAKAYAMA, OKIHIKO, TSUDA, HIROSHI, WATANABE, MASAKI, YAMADA, KIYOMICHI, YATSUGI, YOSHITAKA
Applicants: NISSAN MOTOR, NISSAN MOTOR CO., LTD.
Application year: 1994
Main classification: G08G1
IPC codes: G08G1, G09B29, G01C21